A. Field of the Invention
This invention relates to the subject of mobile Internet Protocol (xe2x80x9cIPxe2x80x9d) data networking.
B. Description of Related Art
Public packet switched networks can be used to carry traffic to and from a mobile communications device, such as a laptop computer or personal digital assistant equipped with a cellular telephone modem. The basic architecture of mobile IP data networking is known in the art and described in several publications, including the Request for Comments document RFC 2002 (1996) and in the textbook of Charles E. Perkins, Mobile IP Design Principles and Practices, Addison-Wesley Wireless Communications Series (1998), the contents of both of which are incorporated by reference herein.
Basically, in Mobile IP communication, a wireless mobile node communicates with a terminal on an IP network by means of a foreign agent and a home agent. Typically, foreign agent functionality is incorporated into a network access server chassis located on a mobile node""s visited network. The foreign agent provides routing services for the mobile node while it is registered with the foreign agent. A Point-to-Point Protocol (PPP) session is established between the mobile node and the foreign agent. The foreign agent de-tunnels and delivers datagrams to the mobile node that were tunneled by the mobile node""s home agent.
The home agent is usually a router on a mobile node""s home network that tunnels datagrams for delivery to the mobile node via the foreign agent when the mobile node is away from home. The home agent maintains current location information for the mobile node, through a variety of possible mechanisms, such as described in the patent application of Richard J. Dynarski, et al., xe2x80x9cDynamic Allocation of Wireless Mobile Nodes Over an Internet Protocol (IP) Networkxe2x80x9d, serial no. 09/233,381, which is incorporated by reference herein. When multiple home agents are handling calls for multiple mobile nodes simultaneously, the home agents are providing, in essence, a service analogous to virtual private network services. Each mobile node is typically associated with a separate home network. The routing path from that home network, through the home agent, to the foreign agent and mobile node is like a virtual private network for the mobile node.
The situation can arise in which two mobile nodes are simultaneously registered with a foreign agent, and have established a PPP session with the foreign agent, but the two mobile nodes have the same home network IP address. In a typical prior art foreign agent implementations the overlapping IP addresses will cause an IP routing failure, since more than one routing table entry could have the same network address associated with different PPP links. This overlapping IP address for both mobile nodes could be a consequence of the home network assigning the same IP address to the mobile node, either a priori or during the mobile IP registration process.
Accordingly, there is a need in the art for a method for handling overlapping IP address pools in a foreign agent. The present invention solves that need and provides methods by which a foreign agent can correctly route packets to a from any number of mobile nodes that are simultaneously registered with the foreign agent but have the same home network IP address.
In a first aspect, a method is provided for routing a data packet through a foreign agent to a wireless node. The method is specifically designed to handle the situation where multiple wireless nodes are registered with the foreign agent but have the same home network IP addresses. The method begins by receiving a data packet at the foreign agent from a home agent associated with wireless node. The foreign agent uniquely associates a home Internet Protocol (IP) address and a home agent IP address contained in the data packet with a Point-to-Point Protocol (PPP) link address. The PPP link address is associated with a PPP link previously established between the foreign agent and the wireless node. This association is preferably implemented in a software table. The foreign agent forwards the data packet through the foreign agent to the PPP link (with the addressing done by reference to the table) for transmission to the wireless node.
In a preferred implementation, the foreign agent maintains a table mapping PPP link addresses to unique pairs of home IP addresses and home agent IP addresses. The step of associating the incoming packet from the home agent is performed automatically in the foreign agent by reference to the table. Since each wireless node having the same home network IP address will have a different home agent, multiple wireless nodes having the same home IP addresses but different home agent IP address may be distinguished from each other in the table and the foreign agent can correctly identify the PPP link to forward the packet to the proper wireless node.
In the reverse direction, the foreign agent receives packets from the wireless nodes, and some of the wireless nodes may have the same home network IP addresses. However, the wireless nodes having the same home network IP address will be associated with a separate PPP link. Be reference to the table, the foreign agent can determine which home agent to forward the packet to, since the home agents are uniquely identified with a home agent IP address and a PPP link address associated with the packet received from the wireless node. The result is that in both directions, the foreign agent can handle the situation where multiple wireless nodes are active in the foreign agent but have the same home network IP address. If conventional IP routing methods were performed, this would not be possible.
These and other features and aspects of the invention will be described in further detail in the following specification.